JPH09236661A - Distance measuring method and distance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measuring device capable of accurately determining a distance to a reflection object without being affected by the strength of reflection wave. SOLUTION: Time width Δt1 corresponding to the reception intensity obtained from time (t11, t12) when a reception waveform L1 is crossing with a threshold value V0, is obtained and then, the time difference Δtc2 from a start pulse to the middle time tc2 of t11 and t22 is obtained. Then, from the time width Δt1 corresponding to the reception intensity, a correction time Δα1 is obtained. With this correction time Δα1, the above time difference Δtc2 is corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to detecting a reflected wave from a reflecting object by radiating a transmitted wave, and detecting the reflected wave from the reflecting object based on the difference between the time when the reflected wave is emitted and the time when the reflected wave is detected. The present invention relates to a distance measuring method and a distance measuring device for calculating a distance.

[0002]

2. Description of the Related Art Conventionally, for example, a pulsed transmission wave such as a light wave or a millimeter wave is intermittently radiated to detect a reflected wave reflected by a reflecting object, and the time when the reflected wave is radiated,
There is known a distance measuring device that calculates the distance to a reflecting object based on the difference from the time when the reflected wave is detected, and the distance to the reflecting object is calculated as follows.

FIG. 16 is a diagram showing the voltage waveform of the reflected wave detected by the wave receiving means. The curve L1 corresponds to a comparatively strong reflected wave, and the curve L2 corresponds to a comparatively weak reflected wave. Corresponding. As illustrated in FIG. 16,
The reflected wave received by the wave receiving means is converted into a voltage according to its intensity, the time from the transmission time when the transmitted wave is radiated until the voltage reaches the predetermined voltage V0 is detected, and at that time, the speed of light / 2. The distance to the reflecting object is calculated by multiplying by. The predetermined voltage V0 is set to avoid the influence of noise components.

However, a predetermined delay time occurs from the time t0 when the wave receiving means receives the reflected wave to the time when the predetermined voltage V0 is reached (time t1, t2). Further, this delay time is affected by the intensity of the reflected wave, and is relatively strong even if the time t0 when the wave receiving means receives the reflected wave is the same time (that is, the distance to the reflecting object is the same). In the curve L1 corresponding to the reflected wave, the voltage reaches V0 at the time t1, whereas in the curve L2 corresponding to the relatively weak reflected wave, the voltage reaches V0 at the later time t2. , A time difference d1 between the times t1 and t2 causes a measurement error.

Therefore, in order to correct the measurement error,
In Japanese Patent Laid-Open No. 3-65678, as shown in FIG. 17, two threshold values (V0, V1) are applied to the received signal waveform.
) Is set, the differential value (ΔV / Δt) of the rising process of the received signal waveform is calculated from the intersection of these two thresholds (V0, V1) and the received signal waveform, and the received wave is derived from this differential value. It has been proposed to suppress the above-mentioned measurement error by calculating the rising time t0.

[0006]

However, the above-mentioned conventional technique has the following problems. That is, in the above-mentioned conventional technique, the differential value (ΔV / Δt) of the rising process of the received signal waveform is calculated, and the differential value (ΔV / Δt) is quantized by an error (continuous amount is discretely calculated). In order to avoid the error caused when expressed by a numerical value) and to calculate with high accuracy, it is necessary to set the time difference Δt to a considerably large value with respect to the sampling time (based on the sampling theorem). As a result, two threshold values (V0 , V1) level difference .DELTA.V must be set to a certain degree.

Further, since noise is superimposed on the received signal, the level difference ΔV between the two threshold values (V0, V1) can be obtained to some extent in order to obtain a differential value with high accuracy without being affected by noise. It needs to be set large. In this way, when the level difference ΔV between the two threshold values (V0, V1) is set to be large, the differential value can be calculated on the curve L1 corresponding to the relatively strong reflected wave as shown in FIG. But
The curve L2 corresponding to the comparatively weak reflected wave has a problem that the differential value cannot be calculated.

[0008] Therefore, an object of the present invention is to provide a distance measuring method and a distance measuring device capable of obtaining a distance to a reflecting object with high accuracy without being affected by the intensity of reflected waves.

[0009]

In order to achieve the above object, the following technical means are adopted. According to the technical means of claim 1, the error correction means obtains the time width during which the signal level of the received wave exceeds the predetermined threshold value, and based on this time width, it is caused by the difference in the intensity of the reflected wave. Correct the distance measurement error to the reflective object. Here, the time width while the signal level of the received wave exceeds the predetermined threshold corresponds to the intensity difference of the received wave, and when the intensity of the received wave is small, the time width becomes small and the intensity of the received wave is large. At times, there is a correspondence relationship in which the time width also becomes large, and this time width is an index that characterizes the reception intensity of the received wave. Therefore, by correcting the distance measurement error based on the time width, it is possible to compensate the distance measurement error to the reflecting object caused by the intensity difference of the received waves.

According to the second aspect of the present invention, the time width calculating means calculates the time width while the signal of the received wave exceeds the predetermined threshold value, and the time difference correcting means is based on the time width. Corrects the time difference measured by the time difference measuring means. This time width characterizes the reception intensity of the received wave, and the relationship between this time width and the correction time (see FIGS. 3 and 8) is obtained in advance by experiments or the like, and the time difference measuring means is used by utilizing this relationship. The time difference measured by As a result, the reception times of the received waves can be set to the same time, and the distance measurement error due to the reception intensity difference of the received waves can be compensated.

According to the third aspect of the present invention, the time width calculating means calculates the time width while the signal of the received wave exceeds the predetermined threshold value, and the distance calculating means is based on the time width. Correct the distance to the reflective object calculated in.
This time width characterizes the reception intensity of the received wave, and the relationship between this time width and the correction distance (see FIG. 14) is obtained in advance by experiments or the like, and is calculated by the distance calculation means using this relationship. Correct the distance to the reflected object.
As a result, it is possible to compensate the distance measurement error to the reflecting object caused by the difference in the intensity of the received waves.

As described in claim 4, the time width calculating means is provided with a signal level determining means for inputting the signal of the received wave to the time measuring means while the signal level of the received wave exceeds a predetermined threshold value. You may comprise. By adopting the technical means according to claim 5, since the reference time difference calculation means obtains the time difference from the emission of the transmission wave to the intermediate time of the time width, the signal of the reception wave is emitted from the emission of the transmission wave. Since the measurement error included in the time difference until rising to the threshold value and the measurement error included in the time difference from the emission of the transmitted wave to the decrease of the signal of the received wave to the threshold value are averaged, higher accuracy is achieved. The distance to the reflective object can be measured.

The time difference correction means, as in the technical means described in claim 6, is the time difference from the emission of the transmitted wave to the rise of the signal of the received wave to the threshold value or the signal of the received wave falls to the threshold value. You may correct the time difference until it is done based on the time width. By adopting the technical means according to claim 7, another signal level determination means having a threshold value set to a value higher than the threshold value is provided, and the threshold value of the other signal level determination means is used as the signal of the received wave. When the time difference exceeds, the time difference measured by the time difference measuring means is corrected based on the time width exceeding the threshold value. A noise component is superimposed on the received wave due to the effects of thermal noise and noise limit. Therefore, when a relatively strong received wave is received, it is better to obtain the time difference measured by the time difference measurement means and the time width calculated by the time width calculation means with a correspondingly high threshold value because of the noise component. The error can be reduced.

By adopting the technical means according to claim 8, the time width during which the signal level of the received wave exceeds the predetermined threshold value is obtained, and the distance to the reflecting object is corrected based on this time width. By doing so, the same effect as in claim 1 can be obtained. According to the technical means of claim 9, the time difference is corrected based on the time width exceeding the predetermined threshold value, and the distance to the reflecting object is obtained based on the corrected time difference. The same effect can be obtained.

According to the technical means described in claim 10, the time difference from the emission of the transmitted wave to the intermediate time of the time width is
By correcting based on the time width, the same effect as in claim 5 can be obtained. Note that, as in the technical means according to claim 11, the time difference from the emission of the transmission wave to the intermediate time is defined as the time difference from the emission of the transmission wave to the time when the signal level of the reception wave reaches the maximum value. You may correct so that.

According to the twelfth aspect of the present invention, the time difference from the emission of the transmitted wave to the rise of the received wave to the predetermined threshold value or the time difference to the fall of the received wave to the predetermined threshold value is calculated, By correcting this time difference based on the time width, the same effect as in claim 6 can be obtained.
Note that, as described in claim 13, the transmission wave is radiated with a time difference from the emission of the transmission wave to the rise of the reception wave to a predetermined threshold or the time difference from the emission of the reception wave to the predetermined threshold. After that, the time difference between the rising time of the received wave and the rising time may be corrected.

According to the technical means as set forth in claim 14, further, when another threshold value set to a value higher than the predetermined threshold value is provided and the signal of the received wave exceeds the other threshold value. The same effect as in claim 7 can be obtained by correcting the time difference based on the time width in which the received wave exceeds the other threshold value.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the distance measuring device of the present invention is
Description will be given based on one embodiment shown in the drawing. [First Embodiment] FIG. 1 is a schematic configuration diagram showing a distance measuring device 1 according to a first embodiment of the present invention. The distance measuring device 1 of the present embodiment is mounted on an automobile to detect an obstacle (reflective object) in front.

The distance measuring device 1 is constructed as follows with the transmitting / receiving section 31 and the computing section 33 as main parts. As shown in FIG. 1, the transmitter / receiver 31 emits a pulsed laser beam H through a scan mirror 35 and a light emitting lens 37 to a semiconductor laser diode (hereinafter simply referred to as a laser diode) 39 and an obstacle (not shown). The light receiving element 43 receives the laser light H reflected by the light via the light receiving lens 41 and outputs a voltage corresponding to the intensity thereof.

The laser diode 39 is connected to the arithmetic unit 33 via a drive circuit 45, and emits (emits) laser light H in response to a drive signal from the arithmetic unit 33. Further, a mirror 47 is provided on the scan mirror 35 so as to be swingable about a vertical axis, and a drive signal from the arithmetic unit 33 is supplied to the motor drive unit 4.
When input through 9, the mirror 47 swings by the driving force of a motor (not shown). Then, the laser light H is swept and irradiated in front of the vehicle over a predetermined angle in the horizontal plane.

On the other hand, the output voltage of the light receiving element 43 is STC.
After being amplified to a predetermined level via the (Sensitivity Time Control) circuit 51, it is input to the variable gain amplifier 53. The STC circuit 51 will be supplemented. Since the received signal strength is inversely proportional to the fourth power of the distance to the target object, there is a reflector or the like that has a high reflectance at a short distance, and this STC circuit 51 is provided to compensate when the received light strength becomes extremely strong. Has been.

The variable gain amplifier 53 is connected to the arithmetic unit 33 via the D / A converter 55, amplifies the input voltage according to the gain (gain) instructed by the arithmetic unit 33, and outputs it to the comparator 57. To do. The comparator 57 compares the output voltage V of the variable gain amplifier 53 with a predetermined voltage V0,
When V> V0, a predetermined reception signal is sent to the time measuring circuit 6
Enter 1 The signal level determination means of the present invention corresponds to the comparator 57.

A drive signal output from the arithmetic unit 33 to the drive circuit 45 is also input to the time measuring circuit 61, and the drive signal is a start pulse PA and the received light signal is a stop pulse PB. Encode the phase difference between them (ie input time difference) into a binary digital signal,
The value is input to the calculation unit 33. This time measuring circuit 61
Is capable of converting a minute time into a numerical value, and can detect a time difference between respective signals even if there are a plurality of received signals with respect to one emitted laser beam H1. This time measuring circuit 61 corresponds to the time measuring means of the present invention.

As the time measuring circuit 61, for example, an odd number stage ring oscillator in which an odd number of inverter gate delay circuits for inverting and outputting an input signal are connected in a ring shape and a pulse edge is circulated on the ring is used. Can be considered. The phase difference (that is, input time difference) between the two pulses PA and PB is measured as follows. That is, when the start pulse PA is input, the pulse edge is circulated on the ring oscillator, and when the stop pulse PB is input, the pulse edge activated by the start pulse PA is output to any inverter gate on the ring oscillator. The phase difference between the two pulses PA and PB is measured by detecting whether or not it has reached the delay circuit.

The time measuring circuit 61 also has a time resolution correction function for accurate time measurement.
Here, a digital signal is corrected by a completely digital circuit by using a reference signal (for example, a crystal oscillation clock). Conventionally, when a digital circuit is used for time measurement, the clock cycle is used as the resolution. However, the time measuring circuit 61 configured as described above has a much finer resolution than the clock circuit (the two pulse PAs described above). , PB) can be digitized. Therefore, even if there are a plurality of received signals for the emitted laser beam H1 (that is, even if there are two or more stop pulses PB for one start pulse PA), the time difference for each signal is detected. You can do it.

Returning to the explanation of the configuration of FIG.
The distance and direction to the obstacle are calculated based on the input time difference from the time measuring circuit 61 and the swing angle of the mirror 47 at that time. The output voltage V of the variable gain amplifier 53 is also input to the peak hold circuit 63, and the peak hold circuit 63 inputs the maximum value of the output voltage V to the calculation unit 33.

Next, the principle of distance measurement of the distance measuring device 1 thus constructed will be described with reference to FIGS. 2 and 3. FIG. 2 is a received waveform diagram for explaining the principle of distance measurement. L1 shows a received waveform when a relatively strong reflected wave is received, and L2 shows a received waveform when a relatively weak reflected wave is received. It is shown. Further, FIG. 3 is a diagram showing the correspondence between the time width corresponding to the reception intensity and the correction time.

Therefore, the time at which the predetermined voltage V0 (hereinafter referred to as a threshold value) set by the comparator 57 in the rising process of the curve L1 intersects is t11, and the time at which the curve L1 falls in the falling process crosses the threshold V0 is t12. The time difference between t11 and time t12 is Δt1. Further, the time when the curve L2 crosses the threshold value V0 in the rising process is t21, and the curve L2 is
The time at which the threshold value V0 crosses during the trailing edge of 2 is t22,
The time difference between time t21 and time t22 is Δt2.

As is apparent from FIG. 2, the time difference Δt1 corresponding to the strong reflected wave and the time difference Δt corresponding to the weak reflected wave.
Comparing with 2, the relationship of Δt1> Δt2 is established. That is, the time (t11, t) at which the received waveform crosses the threshold value V0.
12, t21, t22) the time difference (Δt1,
The magnitude of Δt2) corresponds to the reception intensity. When the reception intensity is small, the time difference is small (Δt2), and when the reception intensity is large, the time difference is large (Δt1). Therefore, this time difference (Δt1, Δt2) is an index characterizing the intensity of the received waveform. Hereinafter, this time difference is referred to as a time width (Δt1, Δt2) corresponding to the reception intensity.

Further, the intermediate time between the times t11 and t12 is tc2, the intermediate time between the times t21 and t22 is tc1, and the curve L1.
, L2 is the time when the maximum voltage is reached, tP, and the intermediate time tc
The time difference between 2 and the time tp at which the maximum voltage is reached is Δα1, and the time difference between the intermediate time tc1 and the time tp at which the maximum voltage is reached is Δ.
Let α2. The time difference between the intermediate time (tc2, tc1) and the time tp at which the maximum voltage is reached is calculated by the following correction time (Δα1,
Δα 2).

Then, there is a predetermined correspondence between the time width (Δt1, Δt2) corresponding to the above-mentioned reception intensity and the correction time (Δα1, Δα2). That is, as shown in FIG. 3, the correction time tends to monotonically increase as the time width corresponding to the reception intensity increases. Therefore, the correspondence shown in FIG. 3 is obtained in advance by experiments or the like, the correction time is obtained from the time width corresponding to the reception intensity, and the intermediate time (tc2, tc) is obtained based on this correction time.
1) is corrected to the time tp at which the maximum voltage is reached (see the arrow in FIG. 2), and the distance to the reflecting object is measured based on the time difference between the time when the laser diode 39 emits light and the time tp when the maximum voltage is reached.

By doing so, the measurement error due to the difference in the intensity of the reflected wave is corrected by the correction time, and the distance to the reflecting object is measured as the time difference up to the same time tp. The relationship between the time width corresponding to the reception intensity and the correction time may be stored in the ROM of the calculation unit 33 as a map. Next, the operation of the distance measuring device 1 embodying this distance measuring principle will be described with reference to FIGS. 4 and 5 show the time measuring circuit 61 and the arithmetic unit 3.
6 is a flowchart showing the distance measurement processing executed by the third embodiment, FIG.
Is a time chart showing various signals during distance measurement.
In the following description, the case where a relatively strong reflected wave is received will be described, but the same process may be executed when a relatively weak reflected wave is received.

First, as shown in FIG. 4, step 100
(Hereinafter, the step is simply referred to as S), the drive circuit 4
A drive signal is output to 5 to cause the laser diode 39 to emit light. That is, as shown in FIG. 6, the calculation unit 33 outputs a measurement start signal (start pulse PA) for driving the laser diode 39, and the drive circuit 45 generates a primary current based on the measurement start signal. When the primary current is applied to the laser diode 39 (see FIG. 6), the laser diode 39 emits light (see FIG. 6).

In subsequent S110, the laser beam H reflected by the reflecting object (not shown) corresponding to the light emission is received through the light receiving lens 41. And this received laser beam H
Is converted into a voltage corresponding to the intensity by the light receiving element 43, and is amplified to a predetermined level via the STC circuit 51 and the variable gain amplifier 53 (see FIG. 6). The amplified signal is input to the comparator 57 as the output voltage V. The comparator 57 compares the output voltage V with the predetermined voltage V0 and inputs the output voltage V to the time measuring circuit 61 while V> V0 is satisfied.

Next, in S120, the time measuring circuit 61 calculates the time difference ΔT1 between the rising edge PA2 of the start pulse PA and the rising edge PB1 of the stop pulse PB as shown in FIG. Similarly, in S130, the time measuring circuit 61 measures the time differences ΔT1 and ΔT2 between the rising edge PA2 of the start pulse PA and the falling edge PB2 of the stop pulse PB (FIG. 6).
Reference).

The time difference data ΔT1 and ΔT2 measured by the time measuring circuit 61 are stored in the RAM (not shown) of the arithmetic unit 33. Subsequently, in S140, as described with reference to FIG. 2, the time width Δt1 corresponding to the reception intensity obtained from the time (t11, t12) at which the reception waveform L1 intersects the threshold value V0 is obtained based on the mathematical expression 1.

[0037]

[Delta] t1 = [Delta] T2- [Delta] T1 Next, in S150, the time difference [Delta] tc2 from the rising edge PA2 of the start pulse PA to the intermediate time tc2 between the time t11 and the time t12 is calculated based on the mathematical formula 2.

[0038]

## EQU00002 ## .DELTA.tc2 = (. DELTA.T1 + .DELTA.T2) / 2 Then, in S160, the correction time .DELTA..alpha.1 is obtained from the time width .DELTA.t1 corresponding to the reception intensity obtained in S140 based on the map shown in FIG. Then, in S170, S1
The time difference Δtc2 up to the intermediate time tc2 obtained at 50 is S
The rising edge PA of the start pulse PA is corrected by the correction time Δα1 obtained at 160.
The time difference .DELTA.tp from 2 to the time tp at which the received waveform L1 reaches the maximum voltage is obtained based on Equation 3.

[0039]

## EQU00003 ## .DELTA.tp = .DELTA.tc2-.DELTA..alpha.1 At S175, the time difference .DELTA.tp obtained at S170.
The distance to the reflecting object is obtained by multiplying by by the speed of light / 2. The processing of S140 to S170 corresponds to the error correcting means of the present invention, the processing of S140 corresponds to the time width calculating means, the processing of S150 corresponds to the reference time difference calculating means, and the processing of S160 to S170. The process corresponds to the time difference correction means. Further, the processing of S175 corresponds to the distance calculating means of the present invention.

By the way, in this embodiment, when the drive signal from the arithmetic unit 33 is inputted to the scan mirror 35 via the motor drive unit 49, the mirror 47 swings to scan a predetermined area. As a result, the laser beam H is swept and irradiated in front of the vehicle over a predetermined angle in the horizontal plane. Therefore, in S180, it is determined whether or not all of the predetermined areas have been scanned, and the processing of S100 to S175 is repeated until the scanning of all areas is completed.

When the scanning of all areas is completed, it is determined in S190 whether or not distance data exists in S175. Here, if there is no distance data, the process proceeds to S200 and only the information that there is no target object to be stored is stored and the distance data is not output. On the other hand, when it is determined that the distance data exists in S190, the process proceeds to S210, and the distance data is grouped according to the distance. Grouping according to this distance will be described. As described above, in the present embodiment, the laser light is emitted by the scanning method, and the laser diode 3 is used.
Since 9 emits light each time the mirror 47 swings by a predetermined angle, the emission direction of the laser light H also has a predetermined angle (for example, 0.5 degrees).
It is set discontinuously every time. Therefore, it is distinguished as the distance data corresponding to the laser beams H having different emission directions, and as it is, the distance data based on the reflected wave from the same target object is processed as another data as it is. Therefore, the adjacent distance data are grouped together.

It should be noted that the term "proximity" may be defined under various conditions, but if the radiation direction of the laser light H is also taken into consideration and there is very close distance data corresponding to adjacent radiation directions, Grouping is preferred. This is because when the laser light H is reflected back to the rear of the preceding vehicle and returned, a plurality of the laser lights H emitted at every predetermined angle are considered to be reflected to the same vehicle.

In subsequent S220, the distance data grouped in S210 is output as the distance to the target. As described above, in this embodiment, the time width (Δt1, Δt2) corresponding to the reception intensity and the correction time (Δα1,
In order to correct the measurement end time to always be time tp based on the correspondence relationship with Δα 2 (see FIG. 3),
It is possible to eliminate the measurement error due to the difference in the reception intensity of the reflected wave.

Further, the correction time is the time t11 and the time t.
Correction processing is performed with reference to the time difference Δtc2 from 12 to the intermediate time tc2. This time difference Δtc2 is obtained by averaging the time difference ΔT1 up to time t11 and the time difference ΔT2 up to time t12 (see Formula 2).
Since the measurement errors included in 1 and ΔT2 are also averaged, the distance to the reflecting object can be measured with higher accuracy.

In the above embodiment, the time width Δ
The correction time Δα1 is calculated from t1 (S160), and the time difference Δtc2 is corrected based on this correction time Δα1 (S17).
0), distance data is calculated based on the corrected time difference Δtp (S175).
Instead of the processing of ˜175, the processing shown in FIG. 13 may be executed.

That is, in S330 following S150,
The distance data to the reflecting object is obtained by multiplying the time difference Δtc2 up to the intermediate time tc2 by the speed of light / 2. here,
Correspondence between the time widths (Δt1, Δt2) corresponding to the reception intensity and the correction distances (Δβ1, Δβ2) is the same as that shown in FIG. 14))). Therefore, in the following S340, the correction distance Δβ1 is obtained from the time width Δt1 corresponding to the reception intensity obtained in S140 based on the map shown in FIG.

Then, in S350, the distance data calculated in S330 is corrected based on the correction distance β1. As described above, even if the distance data is first calculated based on the time difference Δtc2 and the obtained distance data is corrected, the same effect as that of the above-described embodiment can be obtained.

[Second Embodiment] Next, a distance measuring apparatus 1 according to a second embodiment of the present invention will be described below. In addition,
The configuration of this embodiment is the same as that of the first embodiment, and therefore the description thereof is omitted here. Next, the distance measuring principle of the distance measuring device 1 of the present embodiment will be described based on FIGS. 7 and 8. FIG. 7 is a received waveform diagram for explaining the principle of distance measurement. L1 shows a received waveform when a relatively strong reflected wave is received, and L2 shows a received waveform when a relatively weak reflected wave is received. It is shown. Further, FIG. 8 is a diagram showing a correspondence relationship between the time difference corresponding to the reception intensity and the correction time.

Therefore, as in the first embodiment, the time at which the threshold V0 is crossed during the rising process of the curve L1 is t1.
1, t12 is the time when the curve L1 crosses the threshold V0 in the falling process, and Δt1 is the time difference between the time t11 and the time t12. Further, the time at which the threshold V0 is passed during the rising process of the curve L2 is t21, and the threshold V0 during the falling process of the curve L2.
It is assumed that the time at which it intersects with is t22 and the time difference between time t21 and time t22 is Δt2.

As is apparent from FIG. 7, the time difference Δt1 corresponding to the strong reflected wave and the time difference Δt corresponding to the weak reflected wave.
Comparing with 2, the relationship of Δt1> Δt2 is established. That is, the time (t11, t) at which the received waveform crosses the threshold value V0.
12, t21, t22) the time difference (Δt1,
The magnitude of Δt2) corresponds to the reception intensity. When the reception intensity is small, the time difference is small (Δt2), and when the reception intensity is large, the time difference is large (Δt1). Therefore, this time difference is an index characterizing the intensity of the received waveform. Hereinafter, this time difference is referred to as a time width (Δt1, Δt2) corresponding to the reception intensity as in the first embodiment.

Further, the rising times of the curves L1 and L2 are t0, and the time difference between the rising times t0 and t11 is Δ.
α1, the time difference between the rising time t0 and the time t21 is Δα
Set to 2. The time difference (Δt1, Δt2) between the rising time t0 and the times t11, t21 is referred to as the correction time (Δα1, Δα2) as in the first embodiment. Then
There is a predetermined correspondence between the time difference (Δt1, Δt2) corresponding to the reception intensity and the correction time (Δα1, Δα2). That is, as shown in FIG. 8, the correction time tends to monotonically decrease as the time width corresponding to the reception intensity increases. Therefore, the correspondence shown in FIG. 8 is obtained in advance by experiments or the like, the correction time is obtained from the time width corresponding to the reception intensity, and the times t11 and t21 are set to the rising times of the curves L1 and L2 based on the correction time. t
Corrected to 0 (see arrow in FIG. 8), laser diode 3
The distance to the reflecting object is measured based on the time difference from the time point 9 emits light until time t0.

By doing so, the measurement error due to the difference in the intensity of the reflected wave is corrected by the correction time, and the distance to the reflecting object is measured as the time difference until the same time t0. The relationship between the time width corresponding to the reception intensity and the correction time may be stored in the ROM of the calculation unit 33 as a map. Next, the operation of the distance measuring device 1 embodying this distance measuring principle will be described with reference to FIG. FIG. 9 is a flowchart showing the distance measurement processing executed by the time calculation circuit 61 and the calculation unit 33. In the following description, the case where a relatively strong reflected wave is received will be described, but the same process may be executed when a relatively weak reflected wave is received.

The flowchart shown in FIG. 9 is S140 to S1 of the flowchart (FIGS. 4 and 5) of the first embodiment.
It is executed instead of 75, and S100 to S13.
The processes of 0 and S180 to S220 are the same as those in the first embodiment, and therefore the description thereof is omitted. S2 following S130
30, the received waveform L1 is as described with reference to FIG.
The time width .DELTA.t1 corresponding to the reception intensity obtained from the time (t11, t12) at which .alpha. Intersects the threshold value V0 is obtained based on Equation 1 as in the first embodiment.

In subsequent S240, the correction time Δα1 is obtained from the time width Δt1 corresponding to the reception intensity obtained in S230 based on the map shown in FIG. And S25
At 0, the time difference Δ until the time t11 obtained in S120
By correcting T1 with the correction time Δα1 obtained in S250, the time difference Δt0 from the rising edge PA2 of the start pulse PA to the rising time t0 of the received waveform L1 is calculated according to Formula 4.

[0055]

## EQU00004 ## .DELTA.t0 = .DELTA.T1 -.DELTA..alpha.1 Then, in S260, the time difference .DELTA.t0 obtained in S250.
The distance to the reflecting object is calculated by multiplying by by the speed of light / 2. Thus, in this embodiment, the time width (Δt1, Δt2) corresponding to the received light intensity and the correction time (Δα1, Δ)
Since the measurement end time is always corrected to the time t0 based on the correspondence relationship with α2) (see FIG. 8), the measurement error due to the difference in the reception intensity of the reflected wave can be eliminated.

In the present embodiment, the time difference ΔT1 until the time t11 is corrected to the rising time t0 of the received waveform L1, but the time difference t1 is not limited to this.
The time difference ΔT2 up to 12 may be corrected. Further, as described in detail in the first embodiment, the distance data may be first calculated based on the time difference ΔT1, and the obtained distance data may be corrected.

The processing of S230 to S250 corresponds to the error correcting means of the present invention, of which the processing of S230 corresponds to the time width calculating means, and the processing of S240 to S250 corresponds to the time difference correcting means. Further, the processing of S260 corresponds to the distance calculating means. [Third Embodiment] Next, a distance measuring device 1 according to a third embodiment of the present invention will be described below.

In the first and second embodiments, the input voltage is amplified and output to the comparator 57 according to the gain (gain) instructed by the arithmetic unit 33. The comparator 57 outputs the variable gain amplifier 53. The configuration in which the voltage V is compared with the predetermined voltage V0 and the predetermined reception signal is input to the time measuring circuit 61 when V> V0 is described. On the other hand, in this embodiment, a comparator 65 is added in parallel to the comparator 57. The set voltage V1 of the comparator 65 is V
The output voltage V of the variable gain amplifier 53 is set as 1> V0.
Is compared with V0 in the comparator 57 and a predetermined reception signal is input to the time measuring circuit 61 when V> V0, and the predetermined reception signal is measured in time when V> V1 is compared with V1 in the comparator 65. It is configured to input to the circuit 61. The rest of the configuration is similar to that of the first and second embodiments, and the description is omitted. Further, the comparator 65 corresponds to another signal level determination means of the present invention.

Next, the principle of distance measurement of the distance measuring device 1 thus constructed will be described with reference to FIGS. 11, 12 and 15. 11 is an enlarged view of a received waveform for explaining the principle of distance measurement of the present embodiment, FIG. 12 is a timing chart showing various signals at the time of distance measurement, and FIG. 15 is a flowchart showing the distance measurement processing of the present embodiment. is there.

In the above description of the first and second embodiments,
Although the description has been given based on the ideal reception waveform curves L1 and L2, the actual reception waveform of the distance measuring device 1 has a noise component 67 as shown in FIG.
Are superimposed. The fluctuation width of the noise component 67 is as defined by the envelope 69, and the fluctuation width is the time width (Δt1, Δt2) and the time differences ΔT1, ΔT corresponding to the reception intensity.
When measuring 2, there will be a measurement error. Here, the time t11 when the threshold V0 is crossed in the rising process of the received waveform L1.
When the fluctuation range d2 generated at the time t'11 at which the threshold value V1 crosses in the rising process of the received waveform L1 is compared with the fluctuation range d3 generated at the time t'11, based on the threshold value V1 set to a voltage higher than the threshold value V0 by a predetermined value, Time difference ΔT 'until time t'11
The time width corresponding to the reception strength is determined by 1 (time t'11
And the time t'12) and the measurement error included in the time difference ΔT'1 can be suppressed. This is because the slope of the curve becomes the steepest in the vicinity of the intermediate voltage of the waveform during the rising process of the received waveform L1.

Therefore, in this embodiment, two threshold values V0
, V1 are set, and when the received waveform L1 is a strong received wave that exceeds the threshold V1, the time difference ΔT'1 until the time t'11 is calculated using the threshold V1 that reduces the influence of the measurement error. In the case of a weak received wave in which the waveform L1 does not exceed the threshold value V1, the threshold value V0 is used and the time difference ΔT1 until the time t11.
Ask for.

This processing will be described in more detail with reference to FIGS. 12 and 15. In the case of a strong received waveform in which the received waveform L1 exceeds the threshold value V1, the above first
Similarly to the second embodiment, the time difference ΔT1 between the rising edge PA2 of the start pulse PA and the rising edge PB1 of the stop pulse PB and the time difference ΔT2 between the rising edge PA2 of the start pulse PA and the falling edge PB2 of the stop pulse PB are calculated. The time is measured by the time measuring circuit 61 (S120, S130). further,
For the threshold value V1, the rising edge PA2 of the start pulse PA and the rising edge P of the stop pulse PB
The time difference ΔT'1 with B1 'and the time difference ΔT'2 between the rising edge PA2 of the start pulse PA and the falling edge PB'2 of the stop pulse PB are measured by the time measuring circuit 6.
The measurement is performed at 1 (S125, 135). Then, the time difference data ΔT1, Δ measured by the time measuring circuit 61
T2, ΔT'1 and ΔT'2 are R (not shown) of the computing unit 33.
Stored in AM.

Subsequently, in S137, ΔT'1 and ΔT'2
Is determined and Δ is determined in this determination.
If T′1 and ΔT′2 do not exist, the process proceeds to S140, and the processes of S140 to S175 detailed in the first and second embodiments are executed using the time differences ΔT1 and ΔT2. On the other hand, when it is determined in S137 that ΔT'1 and ΔT'2 exist, the process proceeds to S140 ', and S140' to S17 based on the ΔT'1 and ΔT'2.
5'is executed. In addition, this S140 '~ S17
The process 5'is based on the threshold value V1 for ΔT'1 and ΔT '.
The only difference is that 2 is used, and the processing content is S
The same as 140 to S175. Note that S100 to S1
10 and the processing of S180 to S220 is the first and second
The description is omitted because it is the same as the embodiment.

Note that S140 to 170 and S140 'to
170 'corresponds to the error correction means of the present invention, in which S
The processing of 140 and S140 'corresponds to the time width calculating means, the processing of S150 and 150' corresponds to the reference time difference calculating means, and S160 to S170 and S160 'to S17.
The processing of 0'corresponds to the time difference correction means. The above S
The processing of 175 and S175 'corresponds to the distance calculating means of the present invention.

As described above, in the present embodiment, the threshold value V1 higher than the threshold value V0 is set, and the received waveform is the threshold value V1.
In the case of a strong received wave that exceeds 1, the distance measurement processing is executed based on the threshold value V1 set to a high value, so that in addition to the effects of the first and second embodiments, noise components cause It is possible to further reduce the measurement error.

The map showing the correspondence between the time width corresponding to the received light intensity and the correction time used in S160 'is the threshold V0 and the threshold V1 with respect to the size of the received waveform.
When the voltage difference between the two is small, one map can be used in common, but when the voltage difference is large with respect to the size of the received waveform, it is necessary to prepare a map corresponding to the threshold value V1.

In the above-described embodiment described above, if the distance to the reflecting object is measured, the control for preventing a rear-end collision is executed based on the measured distance, or the vehicle ahead follows the vehicle while keeping a predetermined inter-vehicle distance. It can be used for various controls such as follow-up traveling control. Furthermore, the distance measuring device 1 of the present embodiment can be applied to various uses other than being mounted on an automobile.

Further, in the above embodiment, the semiconductor laser diode 19 emits the pulsed laser light H to detect the obstacle, but other than that, it is also possible to use radio waves or ultrasonic waves. Good. Also in this case, the same operation and effect as those of the above-described embodiment can be obtained. That is, an appropriate transmission wave may be selected according to the purpose of use of the distance measuring device 1.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a distance measuring device according to first and second embodiments of the present invention.

FIG. 2 is a received waveform diagram for explaining the distance measuring principle of the distance measuring device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a correspondence relationship between a time width corresponding to a reception intensity and a correction time in the first embodiment of the present invention.

FIG. 4 is a flowchart showing distance measurement processing according to the first and second embodiments of the present invention.

FIG. 5 is a flowchart showing distance measurement processing according to the first, second and third embodiments of the present invention.

FIG. 6 is a time chart showing various signals during distance measurement according to the first and second embodiments of the present invention.

FIG. 7 is a received waveform diagram for explaining the principle of distance measurement of the distance measuring device according to the second embodiment of the present invention.

FIG. 8 is a diagram showing a correspondence relationship between a time width corresponding to reception intensity and a correction time in the second embodiment of the present invention.

FIG. 9 is a flowchart showing distance measurement processing according to the second embodiment of the present invention.

FIG. 10 is a schematic configuration diagram showing a distance measuring device according to a third embodiment of the present invention.

FIG. 11 is an enlarged view of a received waveform for explaining the distance measurement principle of the third embodiment of the present invention.

FIG. 12 is a time chart showing various signals at the time of distance measurement according to the third embodiment of the present invention.

FIG. 13 is a flowchart showing a distance measurement process according to another embodiment of the present invention.

FIG. 14 is a diagram showing a correspondence relationship between a time width corresponding to reception intensity and a correction distance in another embodiment of the present invention.

FIG. 15 is a flowchart showing distance measurement processing according to the third embodiment of the present invention.

FIG. 16 is a received waveform diagram showing a distance measuring principle of a conventional distance measuring device.

FIG. 17 is a received waveform diagram showing a distance measuring principle of a conventional distance measuring device.

[Explanation of symbols]

 1 Distance Measuring Device 31 Transmitting / Receiving Unit 33 Computing Unit 35 Scan Mirror 37 Light Emitting Lens 39 Laser Diode 41 Light Receiving Lens 43 Light Receiving Element 45 Drive Circuit 47 Mirror 49 Motor Drive Unit 51 STC Circuit 53 Variable Gain Amplifier 55 D / A Converter 57 Comparator 61 Time measurement circuit 63 Peak hold circuit 65 Comparator H Laser light

Claims (14)

[Claims] 1. A transmitting means for radiating a transmitted wave, a wave receiving means for receiving a reflected wave of the transmitted wave reflected by a reflecting object as a received wave, and the wave transmitting means for radiating the transmitted wave. Distance measuring device comprising a time difference measuring means for measuring a time difference between the wave receiving means and the reception of the received wave, and a distance calculating means for calculating a distance to the reflecting object based on the time difference. In the above, based on the time width while the signal level of the received wave exceeds a predetermined threshold value, an error correction means for correcting a distance measurement error to the reflective object caused by the intensity difference of the received wave is provided. A distance measuring device characterized by the above. 2. The distance measuring device according to claim 1, wherein the error correction means calculates a time width during which the signal of the received wave exceeds the predetermined threshold value, and the time width calculation means. A time difference correction means for correcting the time difference measured by the time difference measurement means based on the width, and the distance calculation means, the distance to the reflecting object based on the time difference corrected by the time difference correction means. A distance measuring device characterized by calculating. 3. The distance measuring device according to claim 1, wherein the error correction means includes a time width calculation means for calculating a time width during which the signal of the received wave exceeds the predetermined threshold value, A distance measuring device that corrects the distance to the reflecting object, which is obtained by the distance calculating means, based on the time width. 4. The distance measuring device according to claim 2 or 3, wherein the time width calculating means measures the time of the signal of the received wave while the signal level of the received wave exceeds the predetermined threshold value. A distance measuring device comprising a signal level determining means for inputting to the means. 5. The distance measuring device according to claim 2, wherein the time difference correction means calculates a time difference from the emission of the transmission wave to an intermediate time of a time width during which the predetermined threshold is exceeded. A distance measuring device comprising: a reference time difference calculating means for correcting the time difference calculated by the reference time difference calculating means based on the time width. 6. The distance measuring device according to claim 2, wherein the time difference correction means is a time difference between the emission of the transmission wave and the rise of the signal of the reception wave to the threshold value or the signal of the reception wave. The distance measuring device is characterized in that a time difference until the value decreases to the threshold value is corrected based on the time width. 7. The distance measuring device according to claim 4, further comprising another signal level determination means having a threshold value set to a value higher than the predetermined threshold value, wherein the signal of the received wave is the other one. When the signal level determining means exceeds the threshold, the distance measuring device corrects the time difference measured by the time difference measuring means based on the time width exceeding the threshold. 8. A distance measuring method for obtaining a distance to the reflecting object by obtaining a time difference between the emission of the transmitting wave and the time when the transmitting wave is reflected by a reflecting object and received as a receiving wave. A distance measuring method, wherein a time width during which the signal level of the received wave exceeds a predetermined threshold value is obtained, and the distance to the reflecting object is corrected based on the time width. 9. The distance measuring method according to claim 8, wherein the time difference is corrected based on a time width during which the predetermined threshold is exceeded, and the distance to the reflecting object is calculated based on the corrected time difference. A method for measuring distance, which comprises: 10. The distance measuring method according to claim 8 or 9, wherein the time difference between the transmission of the transmission wave and the intermediate time of the time width during which the predetermined threshold is exceeded is calculated, and the time difference is calculated. Is corrected based on the time width. 11. The distance measuring method according to claim 10, wherein a time difference between the emission of the transmission wave and the intermediate time is a maximum value of a signal level of the reception wave after the emission of the transmission wave. A distance measuring method, characterized in that correction is made so that there is a time difference until the arrival time. 12. The distance measuring method according to claim 8 or 9, wherein the time difference between the emission of the transmission wave and the rise of the reception wave to a predetermined threshold value or the fall of the reception wave to a predetermined threshold value. Is calculated, and the time difference is corrected based on the time width. 13. The distance measuring method according to claim 12, wherein a time difference from when the transmitted wave is radiated to when the received wave rises to a predetermined threshold or when the received wave falls to a predetermined threshold. A distance measuring method, wherein the time difference is corrected so as to become a time difference from the emission of the transmission wave to the rising time of the reception wave. 14. The distance measuring method according to claim 8, further comprising another threshold value set to a value higher than the predetermined threshold value, and the received wave signal is the other one. When the received wave exceeds the other threshold, the time difference is corrected based on the time width during which the received wave exceeds the other threshold.